1. Field of the Invention
The present invention generally relates to systems and methods for adjusting a time offset of global positioning system (GPS) signals in a code division multiple access (CDMA) mobile phone.
2. Description of Related Art
GPS is a satellite-based radio navigation system. There are 24 GPS satellites orbiting the Earth and transmitting radio signals. Based on measurements of the time that the radio signals travel from one of the GPS satellites to a GPS receiver, the GPS receiver calculates a distance and determines a location in terms of longitude, latitude and altitude. The GPS satellites transmit radio signals on two different carrier frequencies: a primary frequency and a secondary frequency. The radio signals are transmitted at the two different carrier frequencies simultaneously, the radio signals having different carrier frequencies do not interfere significantly with each other due to pseudo-random noise (PRN) code modulation. Since each of the GPS satellites is assigned to a unique PRN code and furthermore, all of the PRN code sequences are unrelated with respect to each other, the radio signals can be separated and detected by using the CDMA technology.
A CDMA mobile phone, which is equipped with a GPS and built-in maps, can be used for tracking purposes. In the CDMA mobile phone, CDMA signals and GPS signals are transmitted and processed simultaneously. However, there is a time offset, between the CDMA signals and the GPS signals because of different transmission paths of the CDMA signals and the GPS signals, the time offset would affect the positioning accuracy of the CDMA mobile phones.
Accordingly, what is needed is a system and method for adjusting a time offset of GPS signals in a CDMA mobile phone, which can adjust the time offset between the CDMA signals and the GPS signals of the CDMA mobile phone.